The nacelle of an aircraft turbojet engine has a number of moving parts, one typical example being the cascade thrust reverser cowl, which moves between a so-called “direct jet” position (which is adopted in particular during flight) and a “reversed jet” position (which is adopted during braking upon landing).
The displacement of these moving parts is commonly obtained using electric actuating means, as disclosed in application PCT/US2004/019260, and which has been shown in FIG. 1 appended hereto.
One such electric actuator comprises a worm 1 on which a nut 3 is screwed, which in turn is secured to an actuation tube 5, the free end of which ends with an eyelet 7.
The eyelet 7 is in turn fastened to a yoke 115 connected to the moving part to be displaced so that the rotation and translation between the yoke 115 and the eyelet 7 along the displacement axis of the screw 1 are eliminated.
Preferably, connecting rods 8 are inserted between the threads of the screw 1 and those of the nut 3, so as to reduce the friction, such that this type of actuator is commonly referred to as a “ball screw.”
The screw 1 has, at its end opposite that of the eyelet 7, a pinion 9 with an oblique toothing cooperating with a master pinion 11, which in turn is directly or indirectly driven by an electric motor.
Under the action of that electric motor, it is possible to pivot the screw 1 in either direction, and thus to translate the nut 3 in either direction, and therefore to extend or retract the tube 5, said tube 5 being rotationally locked by the eyelet 7 and the yoke 115.
These movements of the tube 5 allow it, via its eyelet 7, to act on the part of the nacelle that one wishes to move, such as a cascade thrust reverser cowl (with the understanding that in general there are several actuators of this type to move such a cowl).
If, for certain reasons, the deployment speed of the tube 5 is poorly controlled at the end of the extension thereof, the actuated element, such as a reverser cowl, may come into abutment somewhat abruptly.
However, the entire mechanism for moving the tube 5 (electric motor, pinions, worm, nut, etc.) has significant inertia, and the abrupt abutment of the reverser cowl may result in damaging certain parts of the actuator and the cowl, and in particular parts located in the connecting area of the end of the tube 5 with the cowl.
For that reason, it is known to place a torque limiter 13, for example near the free end of the tube 5, i.e. just before the eyelet 7, as shown in the appended FIG. 1.
Placing such a torque limiter as far “downstream” as possible on the kinematic chain of the actuator relative to the torque generator formed by the electric motor makes it possible to best protect all of the parts of the actuator and the cowl in the event of an abrupt abutment of the actuated part (thrust reverser, for example).
Concretely, when such an abrupt abutment occurs, the kinematic energy stored by all of the mobile parts of the actuator can dissipate by friction or deformation of the members forming the torque limiter 13, depending on the nature of that limiter.
It should be noted that this limiter can be of the ball and spring, lug shearing, toothed, sliding, or other type.
In all cases, such a torque limiter is complex, bulky, heavy and difficult to calibrate precisely.